use checksum instead of mtime for caching to enable CI caching

[ashanbrown]

The version of ESLint you are using.
Latest.

The problem you want to solve.
I want to be able to restore an eslint cache file from a cache on CI and speed up my build.

Your take on the correct solution to problem.
By storing the checksum of a file instead of the mtime in the cache file, I can restore the eslint cache file from a cache in CI and use it shave about 30 seconds off my build time in a repo I'm currently working with. My understanding is that mtime is not set to anything meaningful during a git checkout and that the processing effort required to restore mtime to the git modification time would defeat much if not all of the value of a cached eslint cache file. This could be an optional step, where we continue to allow mtime for faster local caching but have an option to store a chksum for use with CI (and let that chksum take precedence over mtime).

Are you willing to submit a pull request to implement this change?
If I have to, I guess. ;) Sure, why not.

[aladdin-add]

related: #11314

https://github.com/royriojas/file-entry-cache/commit/343b340847408afc321d942f90ab0ec5c1d1501b#diff-2ea7ee6033c7ced693a37e8ab9b18151

[nzakas]

@aladdin-add it looks like you're saying that the new version of file-entry-cache already uses a checksum?

[aladdin-add]

yes, file-entry-cache>=3.0.0 has made the change.

file-entry-cache@5.0.1 reverted the change, and made it as optional.

[ashanbrown]

Thought I'd share my workaround for this, which is a script that sets mtime to the md5 chksum:

find -name \*.js | parallel 'touch {} -d "$(date -d \@$((0x$(md5sum {} | cut -b 1-7))))"'

[eslint-deprecated]

Unfortunately, it looks like there wasn't enough interest from the team
or community to implement this change. While we wish we'd be able to
accommodate everyone's requests, we do need to prioritize. We've found
that issues failing to reach accepted status after 21 days tend to
never be accepted, and as such, we close those issues.
This doesn't mean the idea isn't interesting or useful, just that it's
not something the team can commit to.

Thanks for contributing to ESLint and we appreciate your understanding.